/*
 * Copyright (C) 2014 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.graph;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.base.Function;
import com.google.common.base.Functions;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Maps;
import com.google.common.graph.GraphConstants.Presence;
import com.google.errorprone.annotations.Immutable;

/**
 * A {@link Graph} whose elements and structural relationships will never change. Instances of this
 * class may be obtained with {@link #copyOf(Graph)}.
 *
 * <p>
 * See the Guava User's Guide's <a href=
 * "https://github.com/google/guava/wiki/GraphsExplained#immutable-implementations">discussion of
 * the {@code Immutable*} types</a> for more information on the properties and guarantees provided
 * by this class.
 *
 * @author James Sexton
 * @author Joshua O'Madadhain
 * @author Omar Darwish
 * @param <N> Node parameter type
 * @since 20.0
 */
@Beta
@Immutable(containerOf = {"N"})
public class ImmutableGraph<N> extends ForwardingGraph<N> {
    @SuppressWarnings("Immutable") // The backing graph must be immutable.
    private final BaseGraph<N> backingGraph;

    ImmutableGraph(BaseGraph<N> backingGraph) {
        this.backingGraph = backingGraph;
    }

    /** Returns an immutable copy of {@code graph}. */
    public static <N> ImmutableGraph<N> copyOf(Graph<N> graph) {
        return (graph instanceof ImmutableGraph) ? (ImmutableGraph<N>) graph
                : new ImmutableGraph<N>(new ConfigurableValueGraph<N, Presence>(GraphBuilder.from(graph),
                        getNodeConnections(graph), graph.edges().size()));
    }

    /**
     * Simply returns its argument.
     *
     * @deprecated no need to use this
     */
    @Deprecated
    public static <N> ImmutableGraph<N> copyOf(ImmutableGraph<N> graph) {
        return checkNotNull(graph);
    }

    private static <N> ImmutableMap<N, GraphConnections<N, Presence>> getNodeConnections(Graph<N> graph) {
        // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will
        // have
        // whatever ordering the graph's nodes do, so ImmutableSortedMap is unnecessary even if the
        // input nodes are sorted.
        ImmutableMap.Builder<N, GraphConnections<N, Presence>> nodeConnections = ImmutableMap.builder();
        for (N node : graph.nodes()) {
            nodeConnections.put(node, connectionsOf(graph, node));
        }
        return nodeConnections.build();
    }

    private static <N> GraphConnections<N, Presence> connectionsOf(Graph<N> graph, N node) {
        Function<Object, Presence> edgeValueFn = Functions.constant(Presence.EDGE_EXISTS);
        return graph.isDirected()
                ? DirectedGraphConnections.ofImmutable(graph.predecessors(node),
                        Maps.asMap(graph.successors(node), edgeValueFn))
                : UndirectedGraphConnections.ofImmutable(Maps.asMap(graph.adjacentNodes(node), edgeValueFn));
    }

    @Override
    protected BaseGraph<N> delegate() {
        return backingGraph;
    }
}
